The present invention relates to fiber optic probes for use in making on-wafer measurements of the parameters of photodetectors and other optoelectronic test devices.
A previous fiber optic probe for use in making such measurements is shown in Modolo et al., "Wafer Level High-Frequency Measurements of Photodetector Characteristics," Applied Optics, volume 27, pages 3059-3061 (1988). In that probe, an optical fiber is pressure fitted into the grooved periphery of a disc segment mounted on a probe arm so that the fiber extends longitudinally through a bend of 90.degree. around the disc segment and thence to a pulsed optical signal source. To probe a given device, the probing end of the optical fiber is advanced longitudinally toward the surface of the test device until it is approximately 100 micrometers from the surface of the device.
A problem in the use of such a probe arises from the fact that the optical fiber is pressure fitted into the peripheral groove of the disc segment and therefore cannot move longitudinally relative to the disc segment. Thus, as the probing end of the optical fiber is moved longitudinally toward the surface of the test device, any slight overtravel in such movement will cause the end of the fiber to impact against the surface causing possible damage either to the surface or to the fiber end, or both.
Another problem arises from the need to provide the optical fiber in a form that is both easily replaceable and of sufficient length to minimize undesirable multimode light transmission effects that cause nonuniform light distribution at the probing end of the fiber.